Cobalt–iron–oxide (Co–Fe–O) nanoparticles have been prepared by the thermal decomposition in benzyl ether of Fe(acac)₃ and Co(acac)₂ in the presence of a mixture of oleic acid and oleylamine templating (surface capping) ligands, and 1,2-hexadecanediol (HDD) as an accelerating agent. The Co percentage may be tuned by adjusting the amount of Co(acac)₂ precursor without influencing the average particle size or particle size distribution. Counter to prior reports the presence of the HDD accelerating agent results in broader nanoparticle diameter distribution; however, for the smallest average sizes a small amount of HDD appears to be beneficial. The effects of changes in the templating ligand concentration and the relative amounts of oleic acidversusoleylamine have been investigated to optimize particle size distribution. Dilution of all the reagents is detrimental to particle size control. Our method for producing 5 nm Co–Fe–O nanoparticles with narrow distributions has reduced the amount of HDD while simultaneously reducing the reaction time.